The present invention relates to a vibration sensing apparatus and, more particularly, to a device for indicating the location of the point of impact between an object and a member.
When an object impacts a member or vice versa, it is often desirable to determine the location of the point of impact on the member. For example, many sports require a player to strike a ball or other game object with a hand held athletic instrument, such as a bat, racket, or club. The player's success in the sport is often determined by his or her ability to swing the athletic instrument so that a preferred portion of the instrument collides with the game object. This preferred portion of the athletic instrument is generally referred to as the "sweet spot".
Athletic instruments which are hand held and designed to strike a game object contain two vibrational nodes. The first node is located under the player's hands, while the second node is located at the "sweet spot". When the game object impacts the instrument at the "sweet spot", a maximum amount of energy is transferred to the game object with a minimum amount of vibration generated within the instrument. However, if the point of impact occurs at a location other than at the vibrational node or "sweet spot", a damped vibration is generated within the instrument. This damped vibration absorbs much of the energy which was to be transferred to the game object. Thus, the game object is not propelled from the athletic instrument at an optimum velocity. It is therefore advantageous for the player to develop good eye-hand coordination so that the athletic instrument imparts the game object at the "sweet spot".
Sensing devices have been attached to athletic instruments for detecting whether the game object contacts a preselected location on the instrument. R. N. Conrey et al. in U.S. Pat. Nos. 4,101,132 and 4,257,594 disclose an athletic instrument, such as a tennis racket, with electronic sensors for detecting contact or proximity of the game element at a preselected location within the intended contact area. Specifically, optoelectrical sensors, resistance or capacitance change sensors, capacitive phase angle change sensors, piezoelectric or piezoresistive sensors, ambient light change sensors, reflected light sensors and electro-fiber optical sensors are employed to determine when the ball contacts the "sweet spot" of a tennis racket. Circuitry is provided which is responsive to the output from the sensor for providing an audible or audio-visual response when the ball contacts the "sweet spot".
The sensing equipment described by Conrey et al. requires the athletic instrument to be specially retrofitted with the electronic sensors. If optical sensors are employed, they are attached and properly aligned on the racket frame so that when the ball contacts the "sweet spot", the beam of light is broken. The optical sensor is either mounted within a hole formed in the racket frame or attached to the frame with tape which contains conductor paths. The conductor paths are used to electrically connect the sensor to the appropriate circuitry. When piezoelectric or piezoresistive elements are used, they are wound around the racket strings within the "sweet spot". If the ball strikes the strings in close proximity to these elements, the stress induced in the elements produces either a voltage or resistance change. The change in voltage or resistance is monitored with voltage or resistance measuring circuits. These circuits generate a logic "yes" when the characteristics change by a predetermined amount. The logic "yes" then activates a switch which controls a means for producing a response which indicates contact was made with the "sweet spot".
It would be desirable to have a sensing device which could be removably attached to a conventional racket, golf club, baseball bat or the like and avoid the need for a specially designed athletic instrument requiring the placement of sensors in or around the intended contact area. Furthermore, it would be desirable to have a sensing device which could be easily transferred to be used on a variety of different athletic instruments to determine whether the player is making contact with the "sweet spot".